The present invention relates to a circuit, and more particularly to a circuit protecting device capable of interrupting effectively and stably the flow of an electric current at such time when an overload of the electric current takes place.
An overload protective device installed on an electric circuit is for use in preventing a fire, as when the flow of the electric current becomes excessive. A protective device of the bimetallic type is superior to those of the fuse type and the electromagnetic type, in view of the facts that the bimetallic type has no such component part as the fuse that gets burned out and has to be replaced, and that the operation of the component parts of the bimetallic type is smoother than the electromagnetic type, and further that the bimetallic type can be made at a lower cost.
As disclosed in the U.S. Pat. No. 4,363,016 issued to Unger, the prior art electric circuit breaker of the bimetallic type is composed mainly of a slide member 18, a bimetallic blade 35, a spring 25 and a rocker button 24. The bimetallic blade 35 has an end that is fastened securely on a terminal 17 and has another end having thereon a contact 21 which is in contact with a contact 20 of another terminal 16 via an opening 55 of the slide member 18, which has a hollow head portion 58 intended for a trunnion 74 of the rocker button 24 of fit thereinto. The rocker button 24 is coupled with an end of the spring 25 which has another end urging a partition wall 45 of a case 11. The slide member 18 is held securely in place by means of the contact 21 of the bimetallic blade 35 via the opening 55. The distortion of the bimetallic blade 35 causes the contact 21 to move away from the opening 55 at such time when an excessive temperature is generated by a current overload. As a result, the rocker button 24 and the slide member 18 are forced out by the elastic force of the spring 25 until a stop pin 49 urges a partition wall 44. Since the spring 25 is not in alignment with the slide member 18, the spring 25 is subjected to bending. Therefore, the operational efficiency and the service life span of the spring 25 are greatly undermined. In addition, the spring 25 is often dislodged easily during the installation thereof, in view of the fact that the spring 25 urges only the rocker button 24 and is therefore exerted upon by a deviating compression. Moreover, the hollow head portion 58 of the slide member 18 and the rocker button 24 are so structurally complicated as to increase substantially the cost of the molding tools which are used to make the slide member 18 and the rocker button 24.
Another category of the prior art circuit breaker of the bimetallic type is disclosed in the Taiwanese Patent 120840, which overcomes the shortcoming of the circuit breaker of the U.S. Pat. No. 4,363,016 that the spring is not aligned with the slide member. However, the second prior art circuit breaker has a spring 3 that is mounted in a spring slot 23 of an insulation piece 2 in such a manner that the spring 3 is retained securely in place by two protruded columns 24 located respectively at both ends of the spring slot 23. When a contact point 54 of a tongue 53 of an elastic guide piece 5 is put through an opening 22 of the insulation piece 2, the spring 3 often fails to descend along with the insulation piece 2. However, the protruded column 24 located at the lower end of the spring slot 23 descends along with the insulation piece 2, thereby releasing the spring 3. The spring 3 can easily jump out of the spring slot 23, in view of the fact that the bottom end of the spring 3 is no longer restrained by the partition piece 14 at such time when the distortion of the elastic guide piece 5 induced by a current overload causes the contact point 54 to move away from the opening 23.